PHP: merge two arrays while keeping keys instead of reindexing?

I just want to add another possibility of doing a merge while keeping keys.

Besides adding key/values to existing arrays using the + sign you could do an array_replace.

$a = array('foo' => 'bar', 'some' => 'string', 'me' => 'is original');
$b = array(42 => 'answer to the life and everything', 1337 => 'leet', 'me' => 'is overridden');

$merged = array_replace($a, $b);

The result will be:

Array
(
    [foo] => bar
    [some] => string
    [me] => is overridden
    [42] => answer to the life and everything
    [1337] => leet
)

Same keys will be overwritten by the latter array.
There is also an array_replace_recursive, which do this for subarrays, too.

Live example on 3v4l.org

Two arrays can be easily added or union without chaning their original indexing by + operator. This will be very help full in laravel and codeigniter select dropdown.

 $empty_option = array(
         ''=>'Select Option'
          );

 $option_list = array(
          1=>'Red',
          2=>'White',
          3=>'Green',
         );

  $arr_option = $empty_option + $option_list;

Output will be :

$arr_option = array(
   ''=>'Select Option'
   1=>'Red',
   2=>'White',
   3=>'Green',
 );

Considering that you have

$replaced = array('1' => 'value1', '4' => 'value4');
$replacement = array('4' => 'value2', '6' => 'value3');

Doing $merge = $replacement + $replaced; will output:

Array('4' => 'value2', '6' => 'value3', '1' => 'value1');

The first array from sum will have values in the final output.

Doing $merge = $replaced + $replacement; will output:

Array('1' => 'value1', '4' => 'value4', '6' => 'value3');

You can simply 'add' the arrays:

>> $a = array(1, 2, 3);
array (
  0 => 1,
  1 => 2,
  2 => 3,
)
>> $b = array("a" => 1, "b" => 2, "c" => 3)
array (
  'a' => 1,
  'b' => 2,
  'c' => 3,
)
>> $a + $b
array (
  0 => 1,
  1 => 2,
  2 => 3,
  'a' => 1,
  'b' => 2,
  'c' => 3,
)